A terminal such as a personal handyphone system (PHS) and a mobile telephone are typically connected to a network through a base station. In a commercial complex or an underground passage where radio waves hardly reach, and a mountainous region where an ISDN line and an optical line for the base station are hardly installed, there may be installed a relay station which relays radio communication between the base station and a radio terminal. The relay station includes a terminal-side communication unit and a base-station-side communication unit. The terminal-side communication unit communicates with the terminal, and the base-station-side communication unit communicates with the base station. Therefore, the communication between the base station and the terminal is relayed (for example, see JP-A-2012-15867).
Some of the relay stations have a directional antenna which enables the communication with the base station at a remote place (for example, see JP-A-2014-233004). Therefore, in a case where a radio wave environment of the base station installed near is not appropriate, the base station at a remote place in a good radio wave environment can be connected, so that it is possible to provide a more stable communication service.